Description
This 490 page, 1979 GMC Medium and Heavy Duty Truck Service Manual Supplement is a reproduction of the original, out of print manual. This supplement manual provides detailed service information, step-by-step repair instruction and maintenance specifications for 1979 GMC medium and heavy duty trucks.
Information in this Supplement, when used with the Service Manuals listed below, will provide coverage for both Medium and Heavy Duty truck models including the following models:
Truck Models: P4T042, C5D042, B6P042 C6D042, C6D062, W6N042, C7D042, C7D064, W7N042, J8C042, J8C064, J9C042, J9C064, D9K042, D9K064, D9L042, D9L064, N9E042, N9E064, N9FQ42, N9F064
Engine Models: 292, 350, 366, 366, 427, 454, 4-53T
FOR MEDIUM DUTY MODELS use Form No. X-7733 Medium Duty Service Manual (Base Manual)
FOR HEAVY DUTY MODELS use Form No. X-7734 Heavy Duty Service Manual (Base Manual) and X-7735 General Service Manual (8ase Manual)
The information in this Supplement is arranged in the same section sequence as in the X-7733 or X-7734 Service Manual. Refer to the “Table of Contents” in X-7735 for Subject Title and applicable section. With the new 1979 Model designation system, the following chart will aid in identifying vehicles in this Supplement and the 1977 Service Manuals.
| DESCRIPTION | 1979 SERIES | 1977 SERIES | 1977 SERVICE MANUAL |
| FORWARD CONTROL CHASSIS | P4 | P40-45 | X-7733 |
| SCHOOL BUS CHASSIS | B6 | S60 | X-7733 |
| M.D. STEEL CONVENTIONAL CAB | C5-6-7 | C,M 50-65 | X-7733 |
| M.D. STEEL TILT CAB | W6-7 | T60-65 | X-7733 |
| H.D. STEEL CONVENTIONAL CAB | J8-9 | H,J 70-95 | X-7734 |
| H.D. ALUMINUM CONVENTIONAL | N9 | M,N 90-95 | X-7735 |
| H.D. ALUMINUM TILT CAB | D9 | D,F 90-95 | X-7734 |
Table of Contents
General Information and Lubrication
Heating and Air Conditioning
Frame and Cab
Frame and Body Mounts
Cab Maintenance
Steel Conventional Cab
Aluminum Tilt Cab
Aluminum Conventional Cab
Sheet Metal and Fiberglass
Steering, Suspension, Wheels and Tires
Front End Alignment
Steering
Front Axle and Suspension
Rear Suspension
Wheels and Tires
Rear Axle and Propeller Shaft
Rear Axle
Propeller Shaft
Brakes
Hydraulic Brakes
Air Brakes
Parking Brakes
Air Compressor and Governor
Engine
Engine Mechanical
Cooling
Fuel System
Engine Electrical
Emission Controls
Exhaust
Transmission & Clutch
Automatic Transmission
Manual Transmission
Clutch
Cab and Chassis Electrical
Metric Information
Special Tools
Index
NOTE: Refer to the applicable section in this Supplement to determine whether there is supplementary information before servicing any unit’ or system on these vehicles.
Index of Topics
Accelerator Linkage
HD Alum Conv
MD Models
Adjustment
Alignment of Axle to Frame
Antenna Trimmer
Brake
Clutch Linkage
Hood
Idle Mixture – Best Idle Method (For All AIR Emission System Engines – Except 292)
Idle Mixture – Lean Drop Method (For All CCS Emission System Engines (RPO NC7) and All 292 Engines (AIR or CCS))
Pitman Shaft Lash
Push Rod (Brake Pedal)
Push (Brake Pedal) HD Steel Conv Cab
Push Rod (Brake Pedal), Hy-Park System
Seat Mechanism Replacement
Shift Linkage
Shift Linkage (MT654)
Slave Piston
TV Linkage
Wheel Bearing – FF931 and FF933 – Front Axles
Air Compressor & Governor Description
Air Conditioning
Air Fan Clutch Controls on HD Models
Axial Six Cylinder Compressor
Condenser, HD Steel Conv Cab Discharging the System
Charging Station Method (All Models)
Discharging the System – Manifold Gage Set Method (All Models)
Partial Charge, HD Steel Conv Cab Models
Pressure Switch on HD Vehicles Equipped with Hydraulic or Viscous Fan
Some D9 Models with Air Fan Clutch Controls
Suction Throttling Valve Adjustment, HD Steel Conv Cab
Vacuum Generator
Application Valve, Stop Light Switch and Plumbing
Application Valve Plumbing
Steel Tilt Application Valve Pedal
Steel Tilt Tractor Models
Axle Shift System – 2 Speed
Shift Controls
Axle Suspension (Tandem), Description
Reyco 101A
Battery Booster and Jumper Cables, Use of Jump Starting
Bendix Master Cylinder
Master Cylinder Operation Brakes
Bleeding (Air) System Components
Air Dryer & Aftercooler
Alcohol Evaporator
Tractor Protection (Breakaway & Quick Release Valve N-20949)
Trailer Brake Hand Control Valve, N-30107
Assemblies
Brake Adjustments
Type “F” Front Brake
Type “FA” Front Brake (Automatic Adjuster)
Type “FR-3” Rear Brake
Type “FR-3A” Rear Brake (Automatic Adjuster)
Disc
Diagnosis of
Dual Power Operational Checks
Dual Power System
Flushing System
Foundation
Hydraulic Pump Replacement C7 with 4-53T Models
Parking
Internal – Expanding Type (12 x 3)
Introduction
Orscheln Type Brake Lever
Tru-Stop (Disc Type)
Pedal Replacement
HD Steel Conv Cab
Push Rod Adjustment (HD Steel Conv Cab)
Steel Tilt Cab
Cab Replacement
Carburetor Holley – 4150 EG
Rochester (Model ME)
Rochester (Model 2G)
Clutch Application Chart
Clutch Controls
Clutch Linkage Adjustment
Clutch Pedal and Shaft Replacement
Clutch – Self Adjustment Angle Spring (Spicer), Diagnosis of
Component Replacement
Axle Oil Filter and Pump (SQHP Axle)
Inter-Axle Differential Shift Unit
Pinion or Output Shaft Oil Seal
Wear Sleeve (SQHP – SQAR Axle Yokes)
Diagnosis Of:
Alcohol Evaporator
Clutch
Eaton Wheel Lock Control System
EH Pump
AC Modulator
AC Wiring Harness Adapter
Stop Light Switch
Dual Power Brake Booster
Electrical Circuit
Eaton Valve Controller
Eaton Controller Terminal Chart
Electro-Hydraulic Brake System Switches & Relay Alum Conv Cab
Electro-Hydraulic Brake System Switches & Relay HD Steel Conv Cab
Electro-Hydraulic Brake System Wiring Harness – Alum Conv Cab
Electro-Hydraulic Brake System Wiring Harness – HD Steel Conv Cab
External Wheel Speed Sensor
Power Cable Assembly
Replacement
Ac Electronic Computer
AC Modulator Solenoid
Eaton Controller Logic Center
Eaton Valve Controller
Solenoid
EH Pump
Stop Light Switch
Wheel Speed Sensor
Sensor Cable
Stop Light Switches – Alum Conv Cab
Wheel Lock Control System
Disc Brake
Dual Power Brake System
Engine Brake Trouble
Evaporation Control System (ECS)
Exhaust System
Hydraulic Boost System
Hydraulic Brake Booster System
Pump Diagnosis
Hydraulic Pump
Diagnosis Schematics
Hy-Park System
Self-Adjusting Angle Spring Clutch (Spicer)
Disc Brakes
Introduction
Operation
Dual Power Brake Operational Checks
Dual Power Brake System
Introduction
Operation
Electrical Odb
Antenna Trimmer Adjustment
Blower Motor Noise Suppression
CB Transceiver Antenna
Diagnosis of Radio Noise
Directional Signal Control Assembly
Electrical Equipment Panel
Engine Noise Suppression
Exhaust Pyrometer Gage
Fiber Optic Illumination
Generator Noise Suppression
Low Vacuum Warning System and Gauge HD
Radio and Transceiver System Wiring Harness Replacement
CB Transceiver
Directional Signal Control Switch
Exhaust Pyrometer Gage
Rear Speaker
Tachograph
Switch Noise Suppression
Tachograph Instrument
Trac-Pack System
Chassis
Back-Up Light Switch
Diagnosis of Electro-Hydraulic Pump
Electro-Hydraulic Pump
Forward Light Wiring Harness
Low Air Pressure Switch
Neutral Safety Switch
Park & Directional Signal Light Assembly Replacement
Park & Directional Signal Light Assembly
Single Sealed-Beam
Miscellaneous Circuits
Circuit Malfunctions
Circuit Protection
Diagnostic Equipment
Diagnostic Meter
Fusible Links
Maintenance and Repair Vehicle Wiring System
Wiring Harness and Wires
Engine Brake (Cummins Diesel) Description and Operation
Engine Brake Maintenance
Engine Governors
Engine Servicing
Engine Water Pump
Front End Drive Power Take-Off Heavy Duty
Medium Duty
Gasoline and Diesel Engine Motor Mounts
Rocker Arm Cover Replacement
366/427 V8 Engine Manifold Replacement
Engine Tune-Up Decals
Emission Controls (Description)
Emission Schematics
Exhaust
Description
Exhaust System Clamps and Couplings
Stainless Steel Exhaust Systems
Stainless Steel Insert Pipe
Fan Clutch (Automatic)
Air Controlled
Air Fan Clutch on Cummins Engine Models
Fluid Fan Clutch Control and Operation
Fluid Fan Clutch Replacement
Fluid Fan Drive System With A/C
Flushing Brake System
Foundation Brakes
Rockwell “S” Cam Type “Q” Series Brake
Frame
Front End Alignment
Front Wheel Bearings
Fuel System
Diesel Engine Air Cleaners
Fuel Tank
M.D. Fuel Tanks
H.D. Alum. Conv. Models with Accelerator Linkage
Holley Carburetor 4150EG
Idle Mixture Adjustment
M.D. Accelerator Linkage
Rochester Carburetor (Model ME)
Rochester Carburetor (Model 2G)
Gasoline Application Chart
General Information
Engine Serial Number
Model Designation
Towing Procedure
Vehicle Identification Number
Governor Elec. Controller & Solenoid Control Valve
Controller & Solenoid Diagnosis
Description
Governor Elec. Controller Test
Overspeed Warning System
1978 Governor System Specifications and Operating Characteristics
1979 Governor System Specifications and Operating Characteristics
Governor System Specifications (V8 Gasoline Engines)
Harness Adapter Circuit Tabulation AC Wiring Harness Adapter Replacement
“Anti Lock” Tell-Tale
Diagnosis of AC Wheel Lock Control with SSI
Diagnosis of Eaton Wheel Lock Control System
Eaton Warning Unit and Wiring Harness
Eaton Warning Unit Replacement H.D. Aluminum Conv. Cab
Hood Adjustment
Hood Hinge Assembly Replacement
Battery Box
Bumper
Dragfoiler
Fender
Grille
Hood Hinge
H.D. Alum. Tilt Cab Replacement
Battery Box
Bumper
Dragfoiler
H.D. Steel Conventional Cab Doors
Insulation Replacement
Check Mechanism
Headliner
Lower Door Trim Panel
Lower Right-Hand Trim Panel Seat
Seat and Seat Support
Upper Right-Hand Trim Panel Seats
H.D. Steel Conventional Cab Dragfoiler
Hood Adjustment (Tilt Hood) Replacement
Assist Handle
Battery Box
Bumper ‘DPT
Dragfoiler
Fender
Fender Extension
Grille
Hood
Hood Check Cable
Hood Hinge
Inner Fender
High Energy Ignition Distributor Replacement
Electronic Module
Ignition Coil
Pick-Up Coil
Hub Caps (Oil Lubricated Bearings)
Hub Cap Disassembly (A & B)
Hydraulic Brake Booster System
Brake System Fluids Caution
Booster Description & Operation
Electro-Hydraulic Pump
Introduction
Hy-Park Chamber Servicing
Chamber Installation
Chamber Removal
Diaphragm & Seal & Apply Piston
Introduction
Hy-Park System
Operation
Important Safety Notice
Interior Trim Panels (Fleet) Replacement
Headliner
Rear Corner Trim Panel
Rear Trim Panel
Interior Trim Panels (Standard) Replacement
Headliner
Lower Rear Trim Panel
Rear Corner Trim Panel
Upper Rear Trim Panel
Lubrication
Diesel Engine Oil Recommendations
Front Suspension Lubrication
Front Wheel Bearing Lubricant
Gas Engine Oil Recommendations
Hydraulic Brakes
Lubrication Details (Auto. Trans.)
Checking the Oil Level
Draining the Transmission Oil
Flushing Oil Cooler & Lines
Governor Primary Oil Screen (AT540 Series)
Governor Secondary Oil Screen (All MT600 Series)
Installing Oil Filter & Pan
Introduction
Oil Filter Removal
Oil Pan Removal
Maintenance, Miscellaneous Items
Care and Cleaning of Interior
Glass-To-Opening Clearance Check
Preventing Water Leaks
Rear Window Replacement
Windshield & Rear Window Sealing
Metric Fasteners
P4, M.D. Conv. Cab & School Bus
M.D. Steel Conv. Cab
Crash Pad Replacement
M.D. Steel Conv. Cab
Hood Check Cable Replacement
M.D. Steel Tilt Cab
Assist Handle Replacement
Oil Lubricated Front Wheel Bearings
Oil Seal Replacement
On-Vehicle Engine Brake Component Replacement and Adjustment
Clutch Switch Mount
Engine Brake Housing Installation
Engine Brake Housing Removal
Fuel Pump Mounting
Fuel Pump Switch Removal
Removal & Installation of Solenoid Valve
Removal of Control Valve Assembly
Slave Piston Adjustment
On-Vehicle Service: Air Compressor & Governor
Compressor Replacement
Pulley Replacement
Disc Brake
Anchor Plate
Bleeding Disc Brake
Brake Rotor (Disc)
Brake Rotor Replacement
Brake Shoe Replacement
Caliper Repair
Disc Brake Service Checks
Metering Valve
Dual Power Brake System
Push Rod Adjustment
Push Rod Length Chart
Brake Pedal & Linkage
Contamination of Brake System
Contamination of Hydraulic Booster System
Dual Power Brake Booster Component Replacement
Dual Power Brake Booster
Replacement
Hydraulic Booster Elec. Circuit
Master Cylinder
Emission Controls
Air Injection Reactor System
Distributor Vacuum Retard Delay System
Evaporation Control System
Throttle Return Control System
TRC Speed
Hydraulic Brake Booster
Bleeding Hydraulic Booster
Booster Assembly Replacement
Contamination of Boost System
Electro-Hydraulic Pump
Flow Switch & Output Push Rod
Hydraulic Pump & Hydraulic System
System Operational Caution
Hydraulic Pumps
P.S. Pump Filter Replacement
P.S. Pump Replacement H.D.
Hy-Park System
Bleeding Hy-Park System
Brake Pedal & Linkage
Brake System Fluids Caution
Caging Hy-Park Chamber
Power Spring
Contamination of Brake System
Contamination of Hy-Park System
Hy-Park Chamber Replacement
Push Rod Adjustment
System Component Replacement
Rear Axle (Tandem)
Differential Carrier Replacement
Rear Suspension
Alignment Adjustment of Axle to Frame
Replacement
Equalizer Assembly Bushing
Radius Rod
Rear Spring
Reyco 101A Tandem Axle Spring
Spring Hanger
Power Steering Gear (Integral)
Integral Gear Bleeding Procedure
Pitman Shaft Lash Adjustment
Relief Valve
Power Steering System Maintenance
Steering Linkage
Dual Power Cylinder Idler
Assembly Replacement
Power Cylinder Replacement
Transmission, Automatic
Shift Linkage Cable Replacement
Shift Linkage Adjustment
TV Linkage Adjustment
Propeller Shafts
1760 Series Universal Joint
1350 Series Universal Joint
Power Steering (Semi-Integral)
Radiator A Shroud In H.D. Conv.
Cab Models with Tilt Hood
Fan Shroud Replacement
Filling A Draining Radiator
Radiator Replacement
Radio Noise, Diagnosis of
Rear Tandem Tag Axle
M.D. Conv. Cab
Tag Axle Replacement
School Bus
Bumper Replacement
Seats (Alum. Tilt Cab)
Seat & Adjustment Mechanism Replacement
Seat Assembly Replacement
Seats A Seat Belts
Replacement
Seat
Seat Belt
Spark Plug Chart
Starting System
Starter Replacement
Steering Column – H.D. Alum. Tilt
Steering Shaft Installation
Steering Shaft Removal
Steering Column – H.D. Steel Conv.
Replacement
Column
Column Support
Column Shaft or Bearing
Steering Shaft
Test Readings
Tire Mounting Caution
Towing Procedure
Trac Pac
Component Replacement
System Components
Transmission
Auxiliary (AT1202)
(H.D. Alum. Conv. Cab)
Shift Lever Replacement
Shift Linkage Adjustment
Transmission Mountings
Transmission Replacement
Fuller, Air System
Air Valve
Range Shift Control Valve
Range Shift Cylinder Seal Replacement
Splitter Control Valve
Replacement
Automatic Trans. (MT654)
Vacuum Power Cylinders
Power Cylinder Air Cleaner
Power Cylinder Replacement
Vacuum Check Valve
Vacuum Gauge
Vacuum Power Brake System Tests
Vacuum Reserve Tank
Vacuum Pump
System Tests
Vacuum Pump Replacement
Vehicle Identification Number
Wheel Bearing Adjustment
-FF931 and FF933 Front Axles
Wheel Cylinders
Wheel Cylinder Repair
Wheel Cylinder Replacement
Windshield Wipers & Washers
Replacement
Washer Control Valve
Wiper Arm
Wiper Blade
Wiper Element
Wiper Motor
Washers
Control Valve Repair
Reservoir and Pump
Pump Inspection
Windshield Washer System Wiper
Control Valves
Control Valve Repair
Motor Air Lines
Motor Repair
Sweep Adjustment
System Air Strainer
